The basic principle behind inerting technology to prevent fires is based on the knowledge that when the equipment within enclosed areas reacts sensitively to the effects of water, the risk of fire can be countered by reducing the oxygen concentration in the relevant area to a value of for example 15% by volume. Most combustible materials can no longer ignite at such a (reduced) oxygen concentration. Accordingly, the main areas of application for this inerting technology in preventing fires also include IT areas, electrical switching and distribution rooms, enclosed facilities as well as storage areas containing high-value commercial goods.
The fire prevention effect resulting from this inerting technology is based on the principle of oxygen displacement. As is known, normal ambient air consists of 21% oxygen by volume, 78% nitrogen by volume and 1% by volume of other gases. For fire prevention purposes, the oxygen content of the spatial atmosphere within the enclosed area is reduced by introducing an oxygen-reduced gas mixture or an oxygen-displacing gas such as for example nitrogen.
Another example of application of the inventive system is in the storing of items, particularly food, preferentially pomaceous fruit, in a controlled atmosphere (CA) in which, among other things, the proportional percentage of atmospheric oxygen is regulated in order to slow the aging process acting on the perishable goods.
Oxygen reduction systems, in particular those used as fire prevention systems, fire extinguishing systems, explosion suppression systems or explosion prevention systems, which create an atmosphere of permanently lower oxygen concentration than the surrounding conditions within an enclosed area, in particular have the advantage—compared to water extinguishing systems such as e.g. sprinkler systems or spray mist systems—of being suited to the extinguishing of the volume. To that end, however, it is necessary to let a precalculated (minimum) volume of oxygen-reduced gas mixture/oxygen-displacing gas into the enclosed area in order to fulfill the intended purpose of the oxygen reduction system of for instance fire prevention, explosion suppression, explosion control or fire extinguishing. Said (minimum) volume of oxygen-reduced gas mixture/oxygen-displacing gas to be let into the area is calculated according to the effective volume and the airtightness of the enclosed area's spatial shell.
The airtightness of the spatial shell of an enclosed area such as, for example, a building envelope, is usually determined by a pressure differential test (blower door test). A fan brought into a spatial shell thereby generates and maintains a constant overpressure and negative pressure of (for example) 50 Pa within the enclosed area. The volume of air escaping through leakages in the spatial shell of the enclosed area is to be forced into the enclosed area by the fan and measured. The so-called n50 value (unit: l/h) indicates how often the interior volume is replaced per hour.
The airtightness determined by a pressure differential test thus corresponds to an air exchange rate contingent on the leakages in a spatial shell of the enclosed area which will also be referred herein to as “feed-independent air exchange rate.” In particular, however, the airtightness determined by a pressure differential test does not factor in an exchange of air involving openings such as doors, gates or windows which can be formed in the spatial shell as needed for the purpose of infeed and/or accessing the enclosed area. This air exchange rate will also be referred herein to as “feed-dependent air exchange rate.”
In contrast to the feed-independent air exchange rate, the feed-dependent air exchange rate cannot normally be determined in advance metrologically since the feed-dependent air exchange rate varies over time and depends on when and how often the spatial shell of the enclosed area is opened for the purpose of infeed and/or accessing, how long the opening formed in the spatial shell of the enclosed area for the purpose of infeed and/or accessing remains, and ultimately how large the opening is.
These parameters determining the feed-dependent air exchange rate normally cannot be determined in advance such that peak values are always assumed with respect to the feed-dependent air exchange rate of the enclosed area when configuring an oxygen reduction system by assuming maximum infeed and/or accessing. Doing so thereby ensures that even in extreme cases, the oxygen reduction system can always provide a sufficient volume of oxygen-displacing gas per unit of time so as to be able to reliably maintain a reduced oxygen content in the spatial atmosphere of the enclosed area below the predefined operating concentration.